Zoom lens

ABSTRACT

A zoom lens, comprises a first lens group, provided in an object side, having a positive refracting power; and a second lens group, provided in an image side from the first lens group, having a negative refracting power; wherein the zoom lens changes magnification by changing a distance between the first and second lens groups, the first lens group comprises a 1a lens subgroup having a negative refracting power, a diaphragm and a 1b lens subgroup having a positive refracting power all arranged in such the order from the object side to the image side; and the zoom lens satisfies the following conditions: 
     
         0.7&lt;L/f.sub.T &lt;1                                           (1) 
    
     
         2.0&lt;f.sub.T /f.sub.1 &lt;4.2                                  (2) 
    
     
         0.1&lt;f.sub.1 /|f.sub.1a |&lt;0.6             (3) 
    
     in which L represents a distance between the image focal point of the zoom lens and an object side surface of the first lens group at a telephoto end position, f T  represents a focal length of the zoom lens at the telephoto end position, f 1  represents a focal length of the first lens group, and f 1a  represents a focal length of the 1a lens subgroup.

BACKGROUND OF THE INVENTION

The present invention relates to a zoom lens, and more particularly, toa compact 2-group zoom lens, especially, to a zoom lens composed of lesslens elements, the zoom lens is suitable for a camera lens of a lensshutter camera.

Recently, the demand for down-sizing a zoom lens of a lens shuttercamera is increasing. To meet the demand, TOKKAISHO 62-90611 andTOKKAIHEI 6-160713, for example, disclose a 2-group zoom lens havingtherein a first lens group that is provided therein with a diaphragm andhas a positive refracting power and a second lens group that has anegative refracting power both arranged in this order from the objectside. In the case of an inner diaphragm type (having a diaphragm in afirst lens group), it is easy to down-size a total length without makingthe refracting power of each group be greater, because a first lensgroup and a second lens group can be close sufficiently to each other ata telephoto end position.

In the conventional example mentioned above, however, there is a problemthat a telephoto ratio is not less than 1 and down-sizing is notsufficient.

SUMMARY OF THE INVENTION

The present invention has been achieved in view of the problemsmentioned above, and its object is to provide a compact zoom lenswherein lens structure in each lens group thereof is establishedappropriately, and thereby its various aberrations are correctedsatisfactorily for the total range of magnifications, while having azooming ratio of about 2-2.4 and a wide field angle.

The object mentioned above can be achieved by the following structures.

Structure 1

A zoom lens composed of a first lens group having positive refractingpower and a second lens group having negative refracting power, both arearranged in this order from the object side and are changed the distancebetween them for changing magnification of the zoom lens, wherein thefirst lens group is composed of 1a lens subgroup having negativerefracting power, a diaphragm and 1b lens subgroup having positiverefracting power all arranged in this order from the object side, andconditional expressions of,

    0.7<L/f.sub.T <1                                           (1)

    2.0<f.sub.T /f.sub.1 <4.2                                  (2)

    0.1<f.sub.1 /|f.sub.1a |<0.6             (3)

are satisfied, under the following conditions.

L: Distance between the image focal point and the surface of a firstlens at a telephoto end position

f_(T) : Focal length of the total system at a telephoto end position

f₁ : Focal length of a first lens group

f_(1a) : Focal length of the 1a lens subgroup

Structure 2

The zoom lens of the invention according to Structure 1, wherein the 1blens subgroup has at least one aspheric surface.

Structure 3

The zoom lens of the invention mentioned above, wherein the 1b lenssubgroup is composed of a single lens having the aspheric surfaces onboth sides and having a positive refracting power.

Structure 4

The zoom lens of the invention mentioned above, wherein the second lensgroup is composed of (2-1)th lens which is made of plastic and has theaspheric surfaces on the single or both side and of (2-2)th lens havingnegative refracting power both arranged in this order from the objectside.

In the invention, a diaphragm is provided in the first lens group toattain down-sizing. In the case of an inner diaphragm type wherein thefirst lens group has therein a diaphragm, a lens barrel tends to becomplicated in terms of structure, compared with a type wherein adiaphragm is located between the first lens group and the second lensgroup. However, it is possible, in the inner diaphragm type, to make thedistance between the two groups be small sufficiently at a telephotoend, because there is no shutter unit between the first lens group andthe second lens group.

In addition to the foregoing, this inner diaphragm type preventseffectively an increase of a front lens diameter that is caused inattaining a wider field angle. Further, the first lens group in theinvention is composed of 1a lens subgroup having a negative refractingpower, a diaphragm and 1b lens subgroup having a positive refractingpower all arranged in this order from the object side, which makes itpossible for the second principal point of the first lens group to besufficiently close to the first principal point of the second lens groupin the case of telephotography. Thus, including an effect of the innerdiaphragm, a sufficient amount of movement is available for the secondlens group, whereby, magnification can be changed for the range from awide angle end position to a telephoto end position without making therefracting power of each lens to be too large, which makes it possibleto correct aberrations in an entire zooming area satisfactorily.

The Condition (1) stated before is a basic condition of the structure ofa zoom lens whose total length at a telephoto end position is short.Namely, when the upper limit of the condition is exceeded, it isdifficult to achieve the down-sizing that is the object of theinvention, while, when the lower limit of the condition is exceeded, itis difficult to keep various aberrations within their allowable ranges.

The Condition (2) is one to stipulate the refracting power of the firstlens group in order to make it compact, while correcting aberrationssatisfactorily under the Condition (1). When the refracting power of thefirst lens group is made larger to exceed the upper limit, residualaberrations in the first lens group are made larger, and further,magnification of the second lens group is made larger, which makes thecorrection of total aberrations be difficult. When the refracting powerof the first lens group is made smaller to exceed the lower limit, atotal length of the lens at the telephoto end position is made larger,which makes it impossible to down-size the zoom lens. The reason for theforegoing is that the total length of the lens at the telephoto endposition L is given by the following expression, when assuming that eachof the first lens group and the second lens group is a single thin lensand a distance between them is represented by e.

    L=e+f.sub.T {1-(e/f.sub.1)}

The preferable is the following condition.

    2.4<f.sub.T /f.sub.1 <3.6

The Condition (3) is one to stipulate the refracting power of the 1alens subgroup. When the negative refracting power of the 1a lenssubgroup is made larger to exceed the upper limit, refracting power ofnegative 1a lens subgroup and that of positive 1b lens subgroup both inthe first lens group are made larger and sensitivity of decentersbetween the groups is increased, which makes the required accuracy forassembling be strict and it causes cost increase. While, when negativerefracting power of the 1a lens subgroup is made smaller to exceed thelower limit, it is difficult to secure the back focal length at a wideangle end position and an effect to correct lateral chromatic aberrationgenerated in the negative second lens group is made smaller. Thepreferable Conditional Expression (3) is as follows.

    0.15<f.sub.1 /|f.sub.1a <0.55

In the invention, the 1b lens subgroup mentioned above is caused to havethe aspheric surfaces on the single or both side. By making somesurfaces in the vicinity of a diaphragm to be aspheric surfaces,spherical aberration of higher order and coma flare are correctedsatisfactorily. In the second lens group, especially in the area on thewide angle side, there is a difference of the height of a passing raybetween the paraxis and the margin. However, the use of some asphericsurfaces make it possible to correct marginal aberrations satisfactorilywithout affecting the aberrations on the axis. By moving distortionaberration toward the negative side by means of the aspheric surface, anincrease of positive distortion aberration at the wide angle side can beprevented. In the second lens group, since the diameter of each lens isrelatively large, it is preferable to provide an aspheric surface on thelens having the smallest diameter, for making the aspheric surfaceaccurately, and for that reason, the aspheric surface is provided on the(2-1)th lens in the example.

Though plastics are easily affected by the temperature fluctuationbecause they generally have a greater change in refractive index for thetemperature fluctuation and have a greater coefficient of thermalexpansion, compared with glass, an amount of movement of a focal pointposition for the temperature fluctuation is made smaller by setting therefracting power of a plastic lens to be small in the invention. Forachieving a small amount of movement of a focal point position, it ispreferable that the relation of the refracting power of the (2-1)th lensmade of plastic is in the following condition;

    |f.sub.2 /f.sub.2-1 |<0.6                (4)

provided that f₂ represents a focal length of the second lens group, andf₂₋₁ represents a focal length of the (2-1)th lens. When the refractingpower of the (2-1)th lens is made larger to exceed the upper limit, itis difficult to control variations of an image plane and performancecaused by environmental changes such as changes of temperature andhumidity. The preferable is the following condition.

    |f.sub.2 /f.sub.2-1 |0.2

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of an optical axis of a lens corresponding toExample 1.

FIGS. 2(a), 2(b) and 2(c) show aberration diagrams for sphericalaberration, astigmatism and distortion aberration for each of wide angleend FIG. 2(a), intermediate area FIG. 2(b) and telephoto end FIG. 2(c)corresponding to Example 1.

FIG. 3 is a sectional view of an optical axis of a lens corresponding toExample 2.

FIGS. 4(a), 4(b) and 4(c) show aberration diagrams for sphericalaberration, astigmatism and distortion aberration for each of wide angleend FIG. 4(a), intermediate area FIG. 4(b) and telephoto end FIG. 4(c)corresponding to Example 2.

FIG. 5 is a sectional view of an optical axis of a lens corresponding toExample 3.

FIGS. 6(a), 6(b) and 6(c) show aberration diagrams for sphericalaberration, astigmatism and distortion aberration for each of wide angleend FIG. 6(a), intermediate area FIG. 6(b) and telephoto end FIG. 6(c)corresponding to Example 3.

FIG. 7 is a sectional view of an optical axis of a lens corresponding toExample 4.

FIGS. 8(a), 8(b) and 8(c) show aberration diagrams for sphericalaberration, astigmatism and distortion aberration for each of wide angleend FIG. 8(a), intermediate area FIG. 8(b) and telephoto end FIG. 8(c)corresponding to Example 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention will be explained in detail as follows based upon opticalsystem structure diagrams for lens systems whose structures are shown inFIG. 1, FIG. 3, FIG. 5 and FIG. 7. Incidentally, the invention is notlimited to these examples, but it can be varied variously for reductionto practice within a range wherein the essential points of the inventionare not overstepped.

The lens system related to the invention is represented by a zoom lensthat is composed of a first lens group having positive refracting powerand a second lens group having negative refracting power both arrangedin this order from the object side, a distance between the first lensgroup and the second lens group being varied for changing magnification,wherein the first lens group is composed of the 1a lens subgroup havingnegative refracting power, a diaphragm, and the 1b lens subgroup havingpositive refracting power.

In this case, f represents a focal length of the total system, F_(NO)represents an F number, ω represents a half field angle, r represents aradius of curvature of each surface of a lens, d represents a lensthickness on an optical axis or an interval between lenses, n_(d)represents a refractive index for d line, υ_(d) represents Abbe number,and f_(B) represents a back focal length which is a distance from avertex of a lens surface closest to an object to an image focal point.The symbol "*" given to the surface number shows that the surface isaspherical. The shape of the aspheric surface is expressed by followingExpression 1;

Expression 1 ##EQU1## wherein, in the orthogonal coordinates systemwherein a vertex of an aspheric surface is the origin and X axis is inthe direction of an optical axis, C represents a vertex curvature, Krepresents a conical constant and Ai (i=4, 6, 8, . . . ) represents anaspheric surface coefficient. EXAMPLE 1

FIG. 1 is a sectional view of an optical axis of a lens corresponding toExample 1, and FIG. 2 shows aberration diagrams for sphericalaberration, astigmatism and distortion for each of wide angle endposition (a), intermediate position (b) and telephoto end position (c)corresponding to Example 1.

In FIG. 1, the 1b lens subgroup is composed of a single positive lens.Optical data are shown in "Table 1" and "Table 2".

                  TABLE 1    ______________________________________    f = 24.6 - 33.9 - 46.7    F.sub.NO. = 4.1 - 5.7 - 7.8    2ω = 68.3° - 53.9° - 40.8°    f.sub.B = 5.7 - 14.7 - 27.0    Surface    No.      r       d              n.sub.d                                          ν.sub.d    ______________________________________    1        9.134   1.50           1.54814                                          45.8    2        11.591  1.90    3        -13.355 0.70           1.80518                                          25.4    4        -57.507 2.50    5*       19.365  3.00           1.58313                                          59.5    6*       -10.632 6.70 - 3.46 - 1.10    7*       -36.638 2.00           1.49700                                          55.8    8*       -37.400 5.02    9        -7.821  1.10           1.72916                                          54.7    10       -22.153    ______________________________________     "*" given to Surface No. represents an aspheric surface. A diaphragm is     located 2.1 mm behind the 4th surface.

                  TABLE 2    ______________________________________                      Aspheric surface    Surface No.       coefficient    ______________________________________    5th surface       K = 0.0                      A4 = 3.55590 × 10.sup.-4                      A6 = -1.59678 × 10.sup.-5                      A8 = 5.85032 × 10.sup.-7                      A10 = -4.68799 × 10.sup.-8    6th surface       K = 0.0                      A4 = -4.98895 × 10.sup.-5                      A6 = -1.38253 × 10.sup.-5                      A8 = 6.15923 × 10.sup.-7                      A10 = -4.01522 × 10.sup.-8    7th surface       K = 0.0                      A4 = 2.07113 × 10.sup.-4                      A6 = 7.66979 × 10.sup.-6                      A8 = -2.49047 × 10.sup.-7                      A10 = 3.08102 × 10.sup.-9    8th surface       K = 0.0                      A4 = 8.23996 × 10.sup.-5                      A6 = 5.53243 × 10.sup.-6                      A8 = -1.43795 × 10.sup.-7                      A10 = 1.51245 × 10.sup.-9    ______________________________________

As shown in FIG. 2, all aberrations are corrected satisfactorily,resulting in an excellent lens system.

EXAMPLE 2

FIG. 3 is a sectional view of an optical axis of a lens corresponding toExample 2, and FIG. 4 shows aberration diagrams for sphericalaberration, astigmatism and distortion for each of wide angle endposition (a), intermediate position (b) and telephoto end position (c)corresponding to Example 1. In FIG. 3, the 1b lens subgroup is composedof two positive lenses. Optical data are shown in "Table 3" and "Table4".

                  TABLE 3    ______________________________________    f = 24.7 - 33.9 - 46.8    F.sub.NO. = 4.1 - 5.6 - 7.8    2ω = 69.2° - 53.6° - 40.5°    f.sub.B = 5.4 - 14.2 - 26.7    Surface    No.      r       d              n.sub.d                                          ν.sub.d    ______________________________________    1        13.903  1.50           1.66672                                          48.3    2        19.226  1.80    3        -13.712 0.70           1.84666                                          23.8    4        -32.681 2.60    5        20.140  2.00           1.62299                                          58.2    6        -19.132 0.50     7*      -11.441 1.40           1.58913                                          61.2     8*      -9.098  6.70 - 3.48 - 1.10     9*      -24.000 2.00           1.49200                                          57.0    10*      -24.659 4.96    11       -7.089  1.10           1.72916                                          54.7    12       -17.364    ______________________________________     "*" given to Surface No. represents an aspheric surface. A diaphragm is     located 1.4 mm behind the 4th surface.

                  TABLE 4    ______________________________________                     Aspheric surface    Surface No.      coefficient    ______________________________________    7th surface      K = 0.0                     A4 = -4.47458 × 10.sup.-4                     A6 = 2.26896 × 10.sup.-6                     A8 = -1.18393 × 10.sup.-6                     A10 = 6.56776 × 10.sup.-8    8th surface      K = 0.0                     A4 = -1.59469 × 10.sup.-4                     A6 = -3.79358 × 10.sup.-6                     A8 = 5.38135 × 10.sup.-8                     A10 = 7.64186 × 10.sup.-9    9th surface      K = 0.0                     A4 = 1.61046 × 10.sup.-4                     A6 = 6.09407 × 10.sup.-6                     A8 = -2.69311 × 10.sup.-7                     A10 = 3.57797 × 10.sup.-9    10th surface     K = 0.0                     A4 = -2.73258 × 10.sup.-5                     A6 = 2.33999 × 10.sup.-6                     A8 = -1.30918 × 10.sup.-7                     A10 = 1.36780 × 10.sup.-10    ______________________________________

As shown in FIG. 4, all aberrations are corrected satisfactorily,resulting in an excellent lens system.

EXAMPLE 3

FIG. 5 is a sectional view of an optical axis of a lens corresponding toExample 3, and FIG. 6 shows aberration diagrams for sphericalaberration, astigmatism and distortion for each of wide angle endposition (a), intermediate position (b) and telephoto end position (c)corresponding to Example 3. In FIG. 5, the 1b lens subgroup is composedof two positive lenses. Optical data are shown in "Table 5" and "Table6".

                  TABLE 5    ______________________________________    f = 24.7 - 34.0 - 46.8    F.sub.NO. = 4.1 - 5.6 - 7.8    2ω= 69.1° - 52.9° - 40.2°    f.sub.B = 5.4 - 14.0 - 25.8    Surface    No.      r       d              n.sub.d                                          ν.sub.d    ______________________________________    1        14.129  1.50           1.66672                                          48.3    2        24.826  1.80    3        -14.829 0.70           1.84666                                          23.8    4        -41.122 2.60    5        26.799  2.00           1.62299                                          58.2    6        -25.812 0.50     7*      -14.699 1.40           1.58913                                          61.2     8*      -9.163  6.96 - 3.71 - 1.36     9*      -25.932 2.00           1.49200                                          57.0    10*      -20.526 4.24    11       -7.322  1.10           1.72916                                          54.7    12       -23.179    ______________________________________     "*" given to Surface No. represents an aspheric surface. A diaphragm is     located 1.4 mm behind the 4th surface.

                  TABLE 6    ______________________________________                     Aspheric surface    Surface No.      coefficient    ______________________________________    7th surface      K = 3.14470 × 10.sup.-4                     A4 = -6.45140 × 10.sup.-4                     A6 = -7.98590 × 10.sup.-6                     A8 = -7.57880 × 10.sup.-7                     A10 = 3.42740 × 10.sup.-8    8th surface      K = 5.03530 × 10.sup.-3                     A4 = -3.46960 × 10.sup.-4                     A6 = -7.86930 × 10.sup.-6                     A8 = 5.32570 × 10.sup.-9                     A10 = 8.93500 × 10.sup.-10    9th surface      K = 1.91100 × 10.sup.-4                     A4 = 1.45250 × 10.sup.-4                     A6 = 4.46990 × 10.sup.-6                     A8 = -7.83400 × 10.sup.-8                     A10 = 1.78270 × 10.sup.-9    10th surface     K = 6.34220 × 10.sup.-4                     A4 = -3.13350 × 10.sup.-5                     A6 = 7.55190 × 10.sup.-7                     A8 = -7.44560 × 10.sup.-8                     A10 = 1.23660 × 10.sup.-9    ______________________________________

As shown in FIG. 6, all aberrations are corrected satisfactorily,resulting in an excellent lens system.

EXAMPLE 4

FIG. 7 is a sectional view of an optical axis of a lens corresponding toExample 4, and FIG. 8 shows aberration diagrams for sphericalaberration, astigmatism and distortion for each of wide angle endposition (a), intermediate position (b) and telephoto end position (c)corresponding to Example 4. In FIG. 7, the 1b lens subgroup is composedof two positive lenses. Optical data are shown in "Table 7" and "Table8".

                  TABLE 7    ______________________________________    f = 24.7 - 37.9 - 58.5    F.sub.NO. = 4.1 - 6.3 - 9.6    2ω = 68.9° - 48.3°- 32.8°    f.sub.B = 5.7 - 17.9 - 37.1    Surface    No.      r       d              n.sub.d                                          ν.sub.d    ______________________________________    1        21.072  1.50           1.67003                                          47.3    2        37.909  1.80    3        -14.205 0.70           1.84666                                          23.8    4        -31.218 2.60     5*      59.608  2.00           1.62299                                          58.2    6        -18.658 0.50    7        -11.855 1.40           1.58913                                          61.2     8*      -7.575  7.86 - 3.94 - 1.36     9*      -23.787 2.00           1.49200                                          57.0    10*      -20.949 4.24    11       -7.253  1.10           1.72916                                          54.7    12       -21.690    ______________________________________     "*" given to Surface No. represents an aspheric surface. A diaphragm is     located 1.4 mm behind the 4th surface.

                  TABLE 8    ______________________________________                     Aspheric surface    Surface No.      coefficient    ______________________________________    5th surface      K = -1.76870 × 10.sup.-4                     A4 = -4.88350 × 10.sup.-4                     A6 = -9.08300 × 10.sup.-6                     A8 = -5.43870 × 10.sup.-7                     A10 = -2.26840 × 10.sup.-8    8th surface      K = 2.38310 × 10.sup.-3                     A4 = -9.97550 × 10.sup.-5                     A6 = -3.47560 × 10.sup.-6                     A8 = -2.73340 × 10.sup.-7                     A10 = -8.41970 × 10.sup.-9    9th surface      K = -7.97550 × 10.sup.-3                     A4 = 2.11680 × 10.sup.-4                     A6 = 5.55280 × 10.sup.-6                     A8 = -3.05880 × 10.sup.-8                     A10 = -2.74130 × 10.sup.-9                     A12 = 3.97120 × 10.sup.-11    10th surface     K = -9.23110 × 10.sup.-4                     A4 = 1.71170 × 10.sup.-5                     A6 = 3.02190 × 10.sup.-6                     A8 = -5.19400 × 10.sup.-8                     A10 = -4.43010 × 10.sup.-10                     A12 = -9.44580 × 10.sup.-12    ______________________________________

As shown in FIG. 8, all aberrations are corrected satisfactorily,resulting in an excellent lens system.

Values corresponding to the conditional expressions (1), (2), (3) and(4) mentioned above corresponding to Examples 1, 2, 3 and 4 are shown infollowing "Table 9".

                  TABLE 9    ______________________________________            L      fT       f1   f1a    f2   f2-1    ______________________________________    Example 1            45.8   46.7     17.4 -37.7  -16.8                                             -28131.9    Example 2            46.4   46.8     17.4 -55.1  -16.8                                             68907.9    Example 3            45.0   46.8     17.8 -84.5  -16.5                                             178.4    Example 4            56.3   58.5     17.3 -63.9  -16.1                                             289.6    ______________________________________            Conditional                      Conditional                                Conditional                                        Conditional            Formula (1)                      Formula (2)                                Formula (3)                                        Formula (4)            L/fT      fT/f1     fl/|f1a|                                        f2/|f2-1|    ______________________________________    Example 1            0.98      2.69      0.46    0.00    Example 2            0.99      2.69      0.32    0.00    Example 3            0.96      2.63      0.21    0.09    Example 4            0.96      3.38      0.27    0.06    ______________________________________

Based on the foregoing, the present invention makes it possible toprovide a compact zoom lens suitable for a small-sized camera in which amagnification ratio is in a range of about 2-2.4, and aberrations arecorrected satisfactorily for the entire range of the magnification whilethe wide field angle is being kept.

What is claimed is:
 1. A zoom lens, comprising:a first lens group,provided in an object side, having a positive refractive power; and asecond lens group, provided in an image side from the first lens group,having a negative refracting power, wherein the zoom lens changesmagnification by changing the distance between the first and second lensgroups, the first lens group comprising a 1a lens subgroup having anegative refracting power, said 1a lens subgroup being the most objectside lens subgroup of the first lens group, a diaphragm and a 1b lenssubgroup having a positive refracting power, all arranged in such orderfrom the object side to the image side; and the zoom lens satisfying thefollowing conditions:

    7<F/f.sub.T <1                                             (1)

    2.0<f.sub.T /f.sub.1 <4.2                                  (2)

    0.1<f.sub.1 /|f.sub.1a |<0.6             (3)

in which L represents a distance between the image focal point of thezoom lens and the surface closest to the object side of the first lensgroup at a telephoto end position, f_(T) represents a focal length ofthe zoom lens at the telephoto end position, f₁ represents a focallength of the first lens group, and f_(1a) represents a focal length ofthe 1a lens subgroup, wherein the second lens group consists of a(2-1)th plastic lens having an aspheric surface and a (2-2)th lenshaving a negative refracting power, and the (2-1 )th lens and the(2-2)th lens are arranged in this order from the object side, andwherein a formula |f₂ /f₂₋₁ |<0.2 in which f₂ represents a focal lengthof the second lens group and f₂₋₁ represents a focal length of the(2-1)th lens.
 2. The zoom lens of claim 1, wherein the 1b lens subgrouphas at least one aspheric surface.
 3. The zoom lens of claim 1, whereinthe 1b lens subgroup consists of a single lens having aspheric surfaceson both sides and having a positive refracting power.
 4. The zoom lensof claim 1, wherein the formula f_(T) /f₁ satisfies the followingcondition:

    2.4<f.sub.T /f.sub.1 <3.6


5. The zoom lens of claim 1, wherein the formula f₁ /|f_(1a) | satisfiesthe following condition:

    0.15<f.sub.1 /|f.sub.1a |<0.55.